As illustrated in FIG. 30, a steering apparatus for an automobile is constructed so that rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering unit 2, and as the input shaft 3 rotates, a pair of left and right tie rods 4 are pushed or pulled, applying a steering angle to the front wheels. The steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and with this steering shaft 5 inserted in the axial direction through a cylindrical shape steering column 6, the steering shaft 5 is supported by the steering column 6 so as to be able to rotate freely. Moreover, the front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 by way of a universal joint 7, and the front end section of this intermediate shaft 8 is connected to the input shaft 3 by way of a separate universal joint 9.
Conventionally, in this kind of steering apparatus, a tilt mechanism for adjusting the up/down position of the steering wheel 1 and/or or a telescopic mechanism for adjusting the forward/backward position of the steering wheel 1 according to the size and driving posture of the driver have been widely used. In order to construct the tilt mechanism, the steering column 6 is supported by the vehicle body 10 so as to be able to pivot around a pivot shaft 11 that is located in the width direction. Here, the width direction means the width direction of the vehicle, and corresponds to the left/right direction. A displacement bracket that is fastened to the portion of the steering column 6 near the rear end section is supported by a support bracket 12 that is supported by the vehicle body 10 such that the displacement bracket can displace in the up/down direction and forward/backward direction. Here, the forward/backward direction is the forward/backward direction of the vehicle.
In order to construct the telescopic mechanism that can displace in the forward/backward direction, the steering column 6 is constructed by combining an outer column 13 and an inner column 14 so as to be able to expand and contract freely in a telescopic manner, and the steering shaft 5 is constructed by combining an outer shaft 15 and an inner shaft 16 with a spline fit or the like such that torque can be freely transmitted, and so as to be able to expand and contract freely. In the example illustrated in the figure, in order to reduce the force required for operating the steering wheel 1, an electric power steering apparatus, having an electric motor 17 as the source of assist power, is also assembled in the steering apparatus.
In the case of having a tilt mechanism and telescopic mechanism, except for the case of electric powered mechanisms, the position of the steering wheel 1 can be adjusted and fastened in the adjusted position based on the operation of an adjustment lever. For example, JP2001-322552(A) discloses construction such as illustrated in FIG. 31 and FIG. 32 wherein based on the rotation of an adjustment rod 19 by an adjustment lever 18, a cam member 21 is caused to pivot and displace at the same time as the axial dimension of a cam apparatus 20 is caused to expand or contract. Moreover, JP2002-87286(A) discloses conventionally known construction of a cam apparatus whose axial dimension is expanded or contracted by an adjustment lever. In the case of the conventional construction illustrated in FIG. 31 and FIG. 32, the displacement bracket 22 that is fastened to the outer column 13a is engaged with or disengaged from the support bracket 12a based on the expansion or contraction of the cam apparatus 20. Furthermore, whether or not to allow the inner column 14a to slide with respect to the outer column 13a is switched based on the pivoting displacement of the cam member 21.
The adjustment rod 19 is inserted in the width direction through long holes 24 in the up/down direction that are formed in a pair of left and right support plate sections 23 of the support bracket 12a, and a long through hole 25 in the forward/backward direction that is formed in the displacement bracket 22. When adjusting the up/down position or forward/backward position of the steering wheel 1 (FIG. 30) that is supported by and fastened to the rear end section of the steering shaft 5a comprising an outer shaft 15a and inner shaft 16a, the adjustment lever 18 is pivoted in a specified direction (typically down), causing the dimension in the axial direction of the cam apparatus 20 to contract, which causes the cam member 21 to separate from the outer circumferential surface of the inner column 14a. The cam apparatus 20 comprises: a drive cam 26 that is supported by and fastened to the end section (left end section in FIG. 32) in the axial direction of the adjustment rod 19, which is able to displace along the long holes 24 in the up/down direction and rotate around its own center axis, the drive cam 26 being prevented from rotating and displacing in the axial direction relative to the adjustment rod 19, and a driven cam 27 that is supported by the middle section in the axial direction of the adjustment rod 19 such rotation and axial displacement relative to the adjustment rod 19 is possible.
Alternatively, as in the construction illustrated in FIG. 33, the cam apparatus 20a can be constructed such that the drive cam 26a is supported by the adjustment rod 19a, which can only displace along the long holes 24 in the up/down direction, and is prevented from rotating around its own center axis, such that the drive came 26a can rotate relative to the adjustment rod 19a, however, is prevented from axial displacement; and the driven cam 27a is supported such that relative rotation with respect to the adjustment rod 19a is suppressed, and axial displacement is possible.
In either construction, by rotating the adjustment lever 18 in a specified direction in order to adjust the up/down position or the forward/backward position of the steering wheel 1, as illustrated in FIG. 34A, a convex section 28 that is formed on the drive cam 26 (26a) engages with a concave section 29 that is formed on the driven cam 27 (27a), causing the dimension in the axial direction of the cam apparatus 20 to contract. In this state, the adjustment rod 19 (19a) causes the outer column to displace within the displaceable range inside the long holes 24 in the up/down direction and long hole 25 in the forward/backward direction. As a result, the position of the steering wheel 1, which is supported by and fastened to the rear end section of the steering shaft 5a that is supported inside the outer column 13a so as to be able to rotate freely, is adjusted. After the steering wheel 1 has been moved to a desired position, the adjustment lever 18 is pivoted in the opposite direction from the specified direction, and as illustrated in FIG. 34B, causes the convex section 28 that is formed on the drive cam 26 (26a) to engage with a stepped section 30 that is formed on the driven cam 27 (27a), which causes the dimension in the axial direction of the cam apparatus 20 (20a) to expand. In the case of the construction illustrated in FIG. 31 and FIG. 32, the outer circumferential surface of the inner column 14a is held at the same time by the cam member 21. On the other hand, in the case of the construction illustrated in FIG. 33, the inner diameter of the outer column 13a contracts. As a result, in either construction, the position of the steering wheel 1 after being adjusted is held.
Moreover, construction such as illustrated in FIG. 35 has been known wherein the steering apparatus comprises a mechanism for protecting the driver from impact that occurs during a secondary collision when the driver collides with the steering wheel during a collision accident of the vehicle. In this construction, when a secondary collision occurs, the entire length of the steering shaft 5b and the steering column 6a contract, lessening the impact due to this secondary collision. More specifically, at the same time that the entire length of these members 5b, 6a contracts, the support bracket 12b that supports the outer column 13a breaks away in the forward direction from the vehicle body 10 (FIG. 30), allowing the entire length of the steering column 6a to contract.
In the case of the construction illustrated in FIG. 35, when the inclination angle of the long holes 24a in the up/down direction with respect to a virtual plane A that is orthogonal to the center axis of the steering column 6a is taken to be α, this inclination angle α is less than the inclination angle β of the center axis of the steering column 6a with respect to the forward/backward direction B (installation angle with respect to the vehicle body) (α<β).
When the inclination angle α of the long holes 24 in the up/down direction is less than the installation angle β of the steering column 6a, there is a possibility that, due to the engagement between the adjustment rod 19b and the long holes 24a in the up/down direction, the steering column 6a will displace upward along these long holes 24a in the up/down direction during a secondary collision. In other words, a component of force in a direction that is orthogonal to the center axis of the steering column 6a occurs due to the impact load during a secondary collision. When the installation angle β is greater than the inclination angle α, this component force becomes larger, and when a force acts that is greater than the tightening force between the adjustment rod 19b and the cam apparatus 20 (20a), the adjustment rod 19b displaces upward along the long holes 24a in the up/down direction, and that may cause the steering column 6a to displace upward.
In this way, there is a possibility that as the steering column 6a displaces upward, the collision position of the airbag that is provided in the steering wheel 1 and the driver will be shifted from the proper position, and that a sufficient effect of reducing the impact by the airbag will not be obtained. Particularly in the case of a small driver, there is a possibility that the head of the driver will not be supported by the airbag. Moreover, there is a possibility that the force that acts during a secondary collision will not be efficiently transmitted in a direction that causes the entire length of the steering column 6a to contract, and so absorbing the impact by the entire length of the steering column 6a contracting may not be performed smoothly, or the support bracket 13b may not break away smoothly from the vehicle body 10, resulting in unstable impact absorption.
JP2010-52639(A) discloses technology for preventing displacement in the upward direction of the steering column during a secondary collision, wherein as illustrated in FIG. 36, regardless of the up/down position of the steering wheel 1, the inclination angle α of the long holes 24b in the up/down direction with respect to a virtual plane A that is orthogonal to the center axis of the steering column 6b is made to be greater than the inclination angle β of the center axis of the steering column 6b with respect to the forward/backward direction B (α>β). With this kind of construction, even when a impact force is input to the adjustment rod 19b in a direction toward the vehicle-top side, in order to cause this adjustment rod 19b to displace toward the vehicle-top side, the adjustment rod 19b must be moved back toward the vehicle-rear side along the axial direction of the steering column 6b against the collapsing load that acts at the same time in the axial direction of the steering column 6b toward the vehicle-front side, and so it displacement of the outer column 13a toward the vehicle-top side is prevented and it becomes possible for the airbag to effectively receive and stop the driver.
However, the steering column apparatus that is disclosed in JP2010-52639(A) comprises a telescopic mechanism and a long hole 25 in the forward/backward direction is provided in the displacement bracket 22. Therefore, due to the impact load toward the vehicle-front side that occurs during a secondary collision, the steering column 6b begins to move against the tightening force from the vehicle installation bracket 12c toward the vehicle-front side. In other words, in a state where the friction on the tightening surface that clamps the steering column 6b against the vehicle installation bracket 12c changes from static friction to dynamic friction, the steering column 6b is prevented from displacing upward by the inclined long holes 24b in the up/down direction, so there is a possibility that the function for prevention upward displacement of the steering column 6b will decrease.
Moreover, in the steering column apparatus that is disclosed in JP2010-52639(A), the long holes 24b in the up/down direction are located on the vehicle-bottom side with respect to the center axis line of the steering column 6b. Therefore, the distance from the installation surface of the support bracket 12c for installation to the vehicle body to the adjustment rod 19 is long, and a prying force occurs in a locking capsule 34, so there is a possibility that the support bracket 12c will not break away smoothly from the vehicle body, and that the impact absorption will be unstable.
Furthermore, in the steering column disclosed in JP2010-52639(A), there is also the possibility that the following problems will occur. In other words, the adjustable state wherein the up/down position or the forward/backward position of the steering wheel 1 can be adjusted, and the state of maintain these positions is switched by expanding or contracting the dimension in the axial direction of the cam apparatus 20 (20a) described above. Of the drive cam 26 (26a) and driven cam 27 (27a) of the cam apparatus 20 (20a), one member is supported such that relative rotation with respect to the adjustment rod 19b is possible, and the other member is supported such that relative rotation is not possible. In the case of either construction, the driven cam 27 (27a) engages in the long holes 24b in the up/down direction such that only displacement along the long holes 24b in the up/down direction is possible.
Therefore, as illustrated in FIG. 36, when the up/down position of the steering wheel 1 is in an upward position, then as illustrated by the dot-dashed line x in FIGS. 34A and 34B, the phase of the driven cam 27 (27a) with respect to the drive cam 26 (26a) shifts, and in order to maintain the steering wheel 1 at the adjusted position, the adjustment lever 18a is rotated, the convex section 28 of the drive cam 26 (26a) is brought into contact with the stopper surface 39 of the driven cam 27 (27a), the amount that the adjustment lever 18a rotates before it can no longer rotate becomes small, and the distance D between the tip end section of the adjustment lever 18a and the steering column 6b becomes large.
On the other hand, when the up/down position of the steering wheel 1 is in a downward position, then as illustrated by the dot-dash line y in FIGS. 34A and 34B, the phase of the driven cam 27 (27a) with respect to the drive cam (26) (26a) shifts, the amount that the adjustment lever 18a rotates before it can no longer rotate becomes large (the possible angle of rotation becomes large), and the distance D between the tip end section of the adjustment lever 18a and the steering column 6b becomes small. In this way, the distance between the tip end section of the adjustment lever 18a and the steering column 6b in the state of maintaining the steering wheel 1 at the adjusted position fluctuates according to the up/down position of the steering wheel 1. In this kind of state, the amount that the adjustment lever 18a protrudes from the column cover that covers the steering column apparatus changes, and there is a possibility of giving the driver an uncomfortable feeling.